As the semiconductor technology advances, the devices are becoming more complex and more integrated. The semiconductor devices are being designed with increasing number of inputs/outputs (I/Os), and they are being pushed to operate at much higher frequencies. Having a large number of I/Os necessarily increase the size of the semiconductor die, which is undesirable since miniaturization is also being pushed. Thus, many devices are designed with the I/Os arranged in an area array pattern over the entire active surface of the semiconductor die instead of the traditional arrangement of I/Os around the periphery of the die. By utilizing the entire surface area of the semiconductor die, a larger number of I/Os can be placed on the die without increasing its size. This type of semiconductor die can then be flip-chip mounted directly to a printed circuit (PC) board. Flip-chip technology is well known in the art. However, not all users of these area array semiconductor devices can handle the bare dice without any type of packaging. Thus, these type of semiconductor dice are often packaged by being flip-chip mounted onto a carrier which is typically ceramic. The ceramic carrier has external electrical connections, such as solder balls or pins on its bottom side, for subsequent attachment to the printed circuit board.
Typically, many semiconductor components are mounted on a PC board. These many components are constantly drawing power from a power plane in the printed circuit board. This constant drawing of power creates noise glitches on the V.sub.DD line of each device. The pulse widths of these noise glitches can range from tens of pico seconds to hundreds of nano seconds. As the operating speed of a semiconductor device increases, the actual device pulse width decreases. A problem occurs when the noise pulse width approaches the actual device pulse width--a catastrophic failure of the device can occur. Typical Phase Lock Loop (PLL) circuits are extremely sensitive to the small pulse width noise. Thus, a bypass capacitor is required to filter out the noise at high frequencies. Basically, as the frequency of a signal increases and the pulse width decreases, the impedance of the capacitor decreases and the bypass capacitor acts as a short circuit to these high frequency charges. The dissipation of high frequency charge is related to the value of the capacitor and the subsequent parasitic series inductance and series resistor associated with it.
Having recognized the need for a bypass capacitor for the higher frequency device, different approaches have been implemented to provide this capacitor. For a ceramic carrier having a semiconductor die flip-chip mounted thereon, a separate low inductance chip capacitor must be added to the top surface of the ceramic package. These low inductance chip capacitors are very costly and are actually ineffective at pulse widths in the nano second to sub nano second range due to the added inductance of the capacitor as well as the inductance due to the conductive traces that connect the capacitor to the actual die. This methodology also adds complexity and significant cost to the final assembly.
Another approach at providing a bypass capacitor is to build one within the second level PC board, such as a motherboard or a daughter card. The packaged device is then mounted onto the PC board, and a separate chip capacitor mounted on the ceramic chip carrier is not required. However, this approach is limited by the thickness of the planes in the PC board and the subsequent effective capacitive area of the die due to the relative velocity the electrons can travel through the dielectric material. Additionally, this approach has the disadvantage of a large inductance path from the capacitor to the actual semiconductor die due to the thickness of the PC board. This capacitor would be ineffective for future generation devices that operate in the hundreds of megahertz (&gt;100 MHz) range. While it is possible to fabricate relatively thin planes in PC boards to reduce inductance, this process is expensive for large boards because it requires the use of advanced processes, such as depositing dielectric materials or roll-coating them. Additionally, this process requires the use of exotic materials like interpenetrating polymers, such as Gortex or Zycon, which are not extensively used in the board fabrication industry due to their high cost. The high cost of making advanced PC boards with built-in capacitors may be prohibitive for some applications, such as desktop computers. Yet these computers utilize semiconductor devices that operate at the high frequency ranges and will require bypass capacitors to filter noisy glitches during their operation.
Thus, a need exists for an effective bypass capacitor for area array type semiconductor devices operating at high frequencies, above 100 MHz, that is also cost effective so that they can be implemented in consumer applications.